I do not think you can just load a library like that in .NET without using unmanaged code. Perhaps that is why you are gaving a hard time with VB.net, you may not be able to use umanaged code in VB.NET.
There are, however ways, of creating assemblies which will delegate functions in a DLL, look that up at
http://www.thecodeproject.com -- there are a lot of articles up there on code delegates in .net.